1. Field of the Invention
The present invention relates to a method of forming a metal wiring in a semiconductor device, and more particularly to a method of forming contact plugs in a semiconductor device having different sized contact holes.
2. Description of the Related Art
In semiconductor devices today, as the degree of integration becomes higher, the size of their contact holes became smaller. The integration of semiconductor devices are mainly of reduction in width which causes increase in their aspect ratio. Accordingly, when the metal wiring are formed by the conventional sputtering method, problem such as a break in metal wiring will cause decrease in semiconductor device reliability.
To overcome problems caused by the increase in aspect ratio, forming plugs with tungsten has been recently suggested. To form these tungsten plugs, a tungsten film is deposited thickly on the entire surface of the substrate so as to completely fill contact holes.
However, to form plugs in a semiconductor having different sized contact holes, tungsten films are deposited so that they are thick enough to fill all the contact holes simultaneously. Accordingly, the manufacturing cost increases because more tungsten is necessary. Also, the manufacturing period increases because more time is necessary in order to remove the surplus tungsten film. Moreover, the increased thickness of the tungsten film will increase the stress of underlying layers during the etching process. Also, after the etching process, global aspect on the surface of the tungsten will cause decrease in the reliability of the metal wiring.